Patent GB-1204496-A (GB)
Title: Presensitised lithographic plate
Inventor: WHITEAR BRIAN RONALD DAVID
IPC: G03F7/095
Filed: 1967-01-23
Abstract: 1,204,496. Photographic materials and processes. ILFORD Ltd. Jan.11, 1968 [Jan.23, 1967; March 30, 1967(2); May 9, 1967], Nos. 3392/67; 14632/67; 14634/67 and 21540/67. Headings G2A and G2C. A photographic material used for the production of printing plates comprises a transparent support coated on one side with a silver halide emulsion layer, the other side having a hydrophilic surface and being coated with a light-sensitive layer which produces a negative printing plate on exposure and developement and this layer being sufficiently insensitive that no image is formed on exposure and development of the silver halide emulsion. Alternatively, the silver halide emulsion layer may be replaced by an imagewise exposed and processed silver halide emulsion. Specified light-sensitive layers are bichromated colloid layers containing diazo resins and naphthoquinone diazides, vinyl polymers containing aromatic azide groups, diazidostilbenes, diazonium compounds with gelatine, novolak, acrylic or vinyl polymers or without any polymer, photopolymerizable layers such as acrylamide and N, N-methylene-bis-acrylamide, polyvinyl cinnamate, polyvinylphosphoric monoesters of chalcones, styrene/maleic anhydride copolymers containing a cinnamoyl or chalcone groups, methylene fluorene sulphonic acid or silver halide emulsions of insufficient speed to be effected by the first exposure. In the examples, a polyester support is coated on both sides with a cellulose ester, one cellulose ester layer containing silica which is coated with the negative-working light-sensitive layer, and the other cellulose ester layer being coated with a silver halide emulsion. Both cellulose ester layers are hydrolyzed before coating with the light-sensitive layers. The negative-working layer may be overcoated with a protective novolak or polyvinyl acetate layer. The cellulose ester layers may be replaced by novolak or polyvinyl alcohol layers. The silver halide emulsion or a protective overcoat may contain a developer such as hydroquinone. The material is imagewise exposed and developed to produce a silver image; development may be by applying a viscous solution of developer or actuator (if developer is present in the layer) or by rupturing a pod containing developer or activator or by using a combined developer and fixer solution and care is taken to ensure that the processing chemicals do not contact the other lightsensitive layer. The exposed silver halide emulsion may alternatively be processed in a folder with a transparent top cover using a viscous solution of developer or activator. The second exposure may be made through the transparent cover of the folder and the silver image. The viscous solution may be contained in a pod in the folder and is broken by rollers. The material is now exposed to ultraviolet light through the silver image and the unexposed areas of the negativeworking layer are removed to produce a printing plate. The developer used may also contain a lacquer and consist of benzyl acetate, cyclohexanone, epoxy resin, red pigment, citric acid, melting agents and gum arabic in aqueous solution. If a diazo resin or a diazonium compound is used as the negative-working layer, the developer may contain a coupler. If a silver halide emulsion is used as the negative-working layer, it is the developed and the unexposed areas removed; the tanning developer may be incorporated in the emulsion. A strippable protective layer may be applied to the negative-working layer which is stripped off after exposure of the negative working layer.